Version Info

• Minecraft, 1.12.2-forge-14.23.5.2854
• Core Lib, 1.1.18

Description of the Bug
The mod is using ModLauncher on 1.12.2 forge, when it hasn't even been implemented yet until 1.13+. it should be using LaunchWrapper

Steps to Reproduce
just play 1.12.2-forge-14.23.5.2854 with the mod and read the logs

Screenshots
there are none since the game doesn't even load in the modpack I'm using, i do have a log tho

[15:38:01] [main/ERROR]: Catching
org.spongepowered.asm.service.ServiceInitialisationException: ModLauncher is not available
at org.spongepowered.asm.service.modlauncher.MixinServiceModLauncherBootstrap.bootstrap(MixinServiceModLauncherBootstrap.java:52) ~[supermartijn642corelib-1.0.19-forge-mc1.12.jar:?]
at org.spongepowered.asm.service.MixinService.runBootServices(MixinService.java:79) [malisiscore-1.12.2-6.5.1.jar:1.12.2-6.5.1-SNAPSHOT]
at org.spongepowered.asm.service.MixinService.(MixinService.java:72) [malisiscore-1.12.2-6.5.1.jar:1.12.2-6.5.1-SNAPSHOT]
at org.spongepowered.asm.service.MixinService.getInstance(MixinService.java:92) [malisiscore-1.12.2-6.5.1.jar:1.12.2-6.5.1-SNAPSHOT]
at org.spongepowered.asm.service.MixinService.boot(MixinService.java:102) [malisiscore-1.12.2-6.5.1.jar:1.12.2-6.5.1-SNAPSHOT]
at org.spongepowered.asm.launch.MixinBootstrap.(MixinBootstrap.java:76) [malisiscore-1.12.2-6.5.1.jar:1.12.2-6.5.1-SNAPSHOT]
at org.spongepowered.asm.launch.MixinTweaker.(MixinTweaker.java:44) [malisiscore-1.12.2-6.5.1.jar:1.12.2-6.5.1-SNAPSHOT]
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) ~[?:1.8.0_452-internal]
at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source) [?:1.8.0_452-internal]
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source) [?:1.8.0_452-internal]
at java.lang.reflect.Constructor.newInstance(Unknown Source) [?:1.8.0_452-internal]
at java.lang.Class.newInstance(Unknown Source) [?:1.8.0_452-internal]
at net.minecraft.launchwrapper.Launch.launch(Launch.java:98) [launchwrapper-1.12.jar:?]
at net.minecraft.launchwrapper.Launch.main(Launch.java:28) [launchwrapper-1.12.jar:?]

The mod is using ModLauncher on 1.12.2 forge

How does it use ModLauncher 🤔

I can not replicate the issue with just my core library installed. In the log snippet you show, the file for my core library seems to be named 'supermartijn642corelib-1.0.19-forge-mc1.12.jar'. There is no version 1.0.19 of my core library and the file name should start with a '_' 🤔
My guess from the snippet is that it is using an old version of mixin from 'malisiscore-1.12.2-6.5.1'. Old 1.12 mods use versions of mixin which do not have great compatibility. Hence, newer 1.12 mods package a special mixin version which is compatible with old 1.12 mods as well as newer mods. Typically, the mixin library from the mod which happens to be loaded first is the one used.
Mod load order is usually equivalent to the file ordering from the operating system. Hence, many newer mods prefix the file name with '_' since that gets ordered before most other characters. This forces the mixin packaged with those mods to loaded.